Leadframes including offsets extending from a major plane thereof, packaged semiconductor devices including same, and mehtods of designing and fabricating such leadframes

ABSTRACT

A leadframe including offsets extending from a major plane thereof. The offsets extend from the major plane at a non-perpendicular angle thereto. Preferably, the angle of extension, relative to the major plane, is about 45 degrees or less. The offsets may extend upwardly and/or downwardly from the major plane. The offsets of the present invention are useful for preventing warpage, bowing, skewing, or other distortions of a packaged semiconductor device including same when subjected to high temperatures or changes in temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/942,182, filed Aug. 29, 2001, now U.S. Pat. No. 6,500,697, issuedDec. 31, 2002, which is a continuation of application Ser. No.09/649,247, filed Aug. 28, 2000, now U.S. Pat. No. 6,331,448 B1, issuedDec. 18, 2001, which is a divisional of application Ser. No. 09/082,105,filed May 20, 1998, now U.S. Pat. No. 6,329,705 B1, issued Dec. 11,2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a leadframe which includesoffsets that extend transversely from a major plane thereof.Particularly, the offsets of the leadframe extend from the leadframe ata non-perpendicular angle. More particularly, the offsets of the presentinvention reduce stress in the package by optimally positioning the dieand, thus, prevent or reduce warpage, bending, or skewing of a packagedsemiconductor device into which the offsets are incorporated.

[0004] 2. Background of Related Art

[0005] With reference to FIG. 1, a conventional packaged semiconductordevice 10 typically includes a semiconductor device 14, which is alsoreferred to as a die, leads 26 operatively connected to thesemiconductor device, and a filled-polymer packaging material 16, whichis also typically referred to as an “encapsulant.” Packaging material 16defines a package 18 that surrounds at least a portion of each ofsemiconductor device 14 and its associated leads 26.

[0006] Various types of leadframes have been employed in the packagingof semiconductor devices. FIG. 1 illustrates an exemplary, conventionalleadframe 20, which includes a die paddle 22, a tie bar 24, and aplurality of leads 26 extending at least partially outwardly toward aframe (not shown), or periphery, of leadframe 20. Typically, the leads26 extend through the packaging material 16 of the packagedsemiconductor device 10 and externally thereof in order to facilitatethe establishment of an electrical connection between the leads and acarrier substrate such as a printed circuit board (PCB). Leadframes thatdo not include a die paddle, which are typically referred to as“paddle-less” leadframes, such as “leads-over-chip” (LOC) configuredleadframes and “leads-under-chip” (LUC) configured leadframes, are alsoemployed in conventional packaged semiconductor devices.

[0007] The tendency of a packaged semiconductor device to warp, bend, orskew when subjected to temperature changes or high temperatures, such asduring the solidification of the molten packaging material followingencapsulation or during the operation of the finished packagedsemiconductor device, has long been a concern to designers andmanufacturers of packaged semiconductor devices (“dice”). As the die,packaging material, leads and other packaged semiconductor devicecomponents undergo temperature changes or are subjected to hightemperatures, the diverse coefficients of thermal expansion of thesevarious components may cause the packaged semiconductor device of whichthey are a part to expand, warp, bend, skew, or otherwise distort.Typically, the higher the temperature to which the die, packagingmaterial, leads and other packaged semiconductor device components aresubjected, the greater the tendency toward warpage, bending, or othershape changes in the package. With the ever-increasing circuit densitiesand reduced sizes of state of the art semiconductor devices, theoperating temperatures of many such devices are also ever-increasing.Thus, state of the art packaged semiconductor devices have an increasedtendency for warpage, bending, skewing and other dimensionaldistortions.

[0008] Some packaged semiconductor devices include stiffening elementsto counteract such warpage, bending, or skewing. Exemplary packagedsemiconductor devices that include stiffening elements are disclosed inU.S. Pat. No. 5,644,161 (the “'161 patent”), which issued to Carmen D.Burns on Jul. 1, 1997, and U.S. Pat. No. 5,369,058 (the “'058 patent”),which issued to Carmen D. Burns et al. on Nov. 29, 1994. The stiffeningelements of the '161 and '058 patents are warp-resistant metal layersthat are disposed proximate both of the major surfaces of thesemiconductor device and are substantially coextensive with the majorsurfaces. Such stiffening elements are, however, somewhat undesirablefrom the standpoint that they are separate from the leadframe and,therefore, additional assembly steps are required during packaging ofthe semiconductor device. Thus, packaging costs and the likelihood ofdamaging the semiconductor device during packaging are increased. Sincethese stiffening elements are additional to the leadframe, they may alsoundesirably increase the size of the packaged semiconductor device.Moreover, the stiffening elements of the '161 and '058 patents aresubstantially parallel to the major plane of the leadframe of thepackaged semiconductor device, and thus are not likely to provide anyadded heat sink properties to the packaged semiconductor device.Therefore, these stiffening elements do not counteract warpage, bending,or skewing of the packaged semiconductor device in directions that aresubstantially parallel to a plane in which a substantial portion of theleadframe is located.

[0009] During many conventional packaging processes, such as transfermolding and injection molding processes, a semiconductor device may bedisplaced within a cavity of a mold and the leads bent or disassociatedfrom the semiconductor device by the hydraulic forces of the moltenpackaging material during its introduction into the mold cavity. Thus,the orientation of the semiconductor device relative to the exteriorsurface of the package may be altered. Such displacement of thesemiconductor device may force the semiconductor device against an innersurface of the cavity, which could damage the semiconductor device or,at the least, compromise the integrity of the package. Non-optimalpositioning of a semiconductor device within a package also changes thedesigned balance of the package, which causes residual stresses withinthe package.

[0010] U.S. Pat. Nos. 5,570,272 (the “'272 patent”), which issued toPatrick Variot on Oct. 29, 1996, and 5,692,296 (the “'296 patent”),which issued to Patrick Variot on Dec. 2, 1997, each disclose aleadframe that has been configured to counteract displacement of theleadframe-semiconductor device assembly within a mold during theintroduction of a packaging material into the cavity thereof and whichincludes a heat sink that is exposed to an outer surface of the package.The leadframe of the '272 and '296 patents includes tie bars that extendperpendicularly upward relative to the plane of the leadframe asufficient distance that, when placed within a cavity of a mold, the tiebars will force a heat sink that is disposed beneath the leadframe intocontact with an inner surface of the cavity. As the leadframe ispositioned within a cavity of a mold, the tie bars abut an inner surfaceof the cavity and force the leadframe and heat sink against an oppositeinner surface of the cavity in order to secure the leadframe within thecavity. Thus, as molten packaging material is introduced into thecavity, the perpendicularly extending tie bars resist any tendency ofthe hydraulic force of the molten packaging material to “lift” theassembly in the mold cavity, holding the leadframe and the semiconductordevice carried thereon in place as the packaging material is introducedinto the cavity, and preventing packaging material from covering thebottom surface of the heat sink.

[0011] The perpendicularly extending tie bars of the leadframe of the'272 and '296 patents are, however, somewhat undesirable because, as amold is closed around that leadframe, the tie bar extensions contact theinner surface of the mold cavity, and may exert force thereagainst,which may scratch or otherwise damage the wall surfaces of the cavity.Damaging the interior surfaces of the mold cavity may cause aestheticchanges to the finished packaged semiconductor device, may hinderrelease of the package from the mold, and may adversely affect theability of conventional transfer equipment to properly handle thepackaged semiconductor device during subsequent assembly or testingsteps, which may cause such equipment to drop or otherwise mishandle thepackaged semiconductor device, and thereby increase failure rates.Furthermore, since the tie bars extend perpendicularly from theleadframe, as force is applied to an end of one of the tie bars, the tiebar may flex or bend unpredictably under the longitudinal loading anddisplace the semiconductor device within the cavity. As notedpreviously, such displacement of the leadframe within the cavity offsetsthe leadframe within the finished packaged semiconductor device, whichmay affect the dimensions, the mechanical balance, and the mechanicaland electrical reliability of the packaged semiconductor device. Whenthe packaging material hardens, if these tie bars have been previouslyflexed under force of the closed mold, upon release of the package fromthe mold, the tie bars may exert force on the packaging material, whichmay cause bowing, warpage, bending, or skewing of the packagedsemiconductor device, or cause the packaging material to crack orotherwise separate.

[0012] The leadframe that is disclosed in the '272 and '296 patents isfurther undesirable since the perpendicularly extending offsets thereofprevent compact stacking of such leadframes for storage. Thus, theseleadframes consume excessive space in storage and in the equipment thatfeeds these leadframes into molding equipment relative to the amount ofspace consumed by conventional leadframes that may be compactly stacked.

[0013] Thus, a leadframe is needed that resists warpage, bending,skewing and other distortions when incorporated into a packagedsemiconductor device, and which prevents displacement of an associatedsemiconductor device within a mold cavity during packaging processeswithout damaging interior surfaces of a mold cavity. There is a furtherneed for a leadframe that may be stacked and stored in a relativelycompact manner.

BRIEF SUMMARY OF THE INVENTION

[0014] A leadframe of the present invention may be of a conventional,LOC, LUC, or any other leadframe configuration that is employed in theart. The leadframe according to the present invention includes aplurality of leads extending inwardly therefrom. The leadframe of thepresent invention also includes a plurality of offsets that extendtransversely and non-perpendicularly therefrom relative to a plane uponwhich a substantial portion of a die mounting region of the leadframelies, which may be characterized as the “major plane” of the leadframe.The offsets preferably extend from the leadframe at an angle of about 45degrees or less to this major plane.

[0015] In a first variation of the leadframe of the present invention,each of the offsets extends from the same side of the leadframe. In asecond variation, offsets extend from both sides of the leadframe.Offsets may be specially added to the leadframe to extend from anyportion thereof, or may be incorporated into the structure of anexisting element of the leadframe, such as a lead, tie bar, bus bar, ordie paddle thereof.

[0016] Accordingly, the present invention also includes methods ofdesigning a leadframe with one or more offsets. In designing theleadframe of the present invention, various factors may be considered indetermining the number, location, direction of extension and length ofthe offsets. Such factors include, without limitation, the predictedwarpage tendencies of the particular package-leadframe-semiconductordevice combination and the desired manner in which packaging materialenters and fills a cavity of a mold to surround theleadframe-semiconductor device assembly disposed within the mold cavity.

[0017] A method of packaging a semiconductor device in association withthe leadframe of the present invention includes operatively attachingthe semiconductor device to the leadframe, and positioning theleadframe-semiconductor device assembly in a cavity of a mold, such thatselected ones of the offsets abut or are proximate an interior surfaceof the cavity. As a molten packaging material is injected into the moldcavity, the offsets resist the force of the flow of the molten packagingmaterial traversing the cavity in order to maintain the position of theleadframe relative to the cavity.

[0018] Packaged semiconductor devices that are formed in accordance withthe method of packaging are also within the scope of the presentinvention. The packaged semiconductor device includes the leads andoffsets of the inventive leadframe, a semiconductor device operativelyattached to the leads, and a molded package disposed about at least aportion of the leadframe-semiconductor device assembly. The offsetsextend substantially through the package from the leadframe major planeto a location proximate an exterior surface thereof. An offset may alsoextend to the exterior of the package such that a portion of the offsetis flush with an edge thereof exposed to the package exterior.

[0019] Other advantages of the present invention will become apparent tothose of ordinary skill in the relevant art through a consideration ofthe appended drawings and the ensuing description.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0020]FIG. 1 is a cross-sectional view of a conventional packagedsemiconductor device;

[0021]FIG. 2 is a top plan view of an embodiment of a leadframeaccording to the present invention, including offsets extending from thebottom surface thereof;

[0022]FIG. 2a is a perspective view of a variation of the leadframe ofFIG. 2;

[0023]FIG. 3 is a cross-section taken along line 3-3 of FIG. 2, whichalso illustrates a die disposed upon the leadframe and a packagesurrounding at least a portion of each of the leadframe and die;

[0024]FIGS. 4 and 5 are cross-sectional views of variations of theleadframe of FIGS. 2 and 3, which include offsets extending from the topsurface thereof and from both the top and bottom surfaces thereof,respectively;

[0025]FIG. 6a is a cross-sectional view of another variation of theleadframe of FIGS. 2 and 3, wherein conventional leadframe elements arebent to define the offsets;

[0026]FIG. 6b is a cross-sectional view of yet another variation of theleadframe of FIGS. 2 and 3, wherein the die paddle has four offsetsextending therefrom in a cruciform configuration;

[0027]FIG. 7 is a cross-sectional view illustrating the leadframe ofFIG. 5 disposed within a cavity of a mold;

[0028]FIG. 8 is a cross-sectional view of a packaged semiconductordevice according to the present invention, wherein the offsets extendflush with an exterior surface of the package, and illustrating thepredictable direction in which the offsets will flex if they contact thesurface of the cavity as the mold is closed;

[0029]FIG. 9 is a schematic representation of a plurality ofconventional leadframes including perpendicularly extending offsets thatare stacked one upon another;

[0030]FIG. 10 is a schematic representation of a plurality of theleadframes of FIG. 5, which includes offsets that extend therefrom at anangle of about 45 degrees or less, in a stacked orientation; and

[0031]FIG. 11 is a schematic representation of two adjacent, stackedleadframes which include offsets that extend therefrom at anon-perpendicular angle of greater than about 45 degrees.

DETAILED DESCRIPTION OF THE INVENTION

[0032] With reference to FIG. 2, a first embodiment of a leadframe 30according to the present invention includes a plurality of leads 34 thatextends laterally outward from a die mounting region 32 thereof.Leadframe 30 also includes a plurality of offsets 36 that extendstransversely relative to the plane of die mounting region 32 of theleadframe, at an angle that is non-perpendicular to the die mountingregion. Preferably, offsets extend from leadframe 30 at an angle ofabout 45 degrees or less.

[0033] As depicted in FIGS. 2 and 3, each of offsets 36 extendsupwardly, from major plane 38 of leadframe 30, and is positionedadjacent one or more leads 34. Referring to FIG. 4, in a variation ofleadframe 30, each of offsets 36 extends downwardly from major plane 38.FIG. 5 illustrates another variation of leadframe 30, wherein a firstgroup of offsets 36 a extends upwardly from the major plane 38, and asecond group of offsets 36 b extends downwardly from major plane 40.

[0034] Although FIGS. 2 through 5 illustrate offsets 36 that areadjacent to leads 34, offsets 36 may extend transversely from anotherportion of leadframe 30, such as the die paddle, tie bars, bus bars, orlateral extensions of any of the foregoing.

[0035]FIGS. 2 through 5 illustrate a “leads-over-chip” (LOC) leadframe30 that includes a die mounting region 32 to which a surface 52 of asemiconductor device 50 (see FIG. 3), which is also referred to as adie, is attached. Alternatively, leadframe 30 may have a conventionalconfiguration (i.e., with a die paddle upon which a semiconductor device50 may be disposed), a “leads-under-chip” (LUC) configuration, or anyother type of leadframe configuration known in the art. Selected leads34 are electrically connected to corresponding bond pads 54 ofsemiconductor device 50 by techniques that are known in the art,including, without limitation, by wire bonding, TAB bonding, z-axisconductive elastomer, solder, or conductive epoxy (see FIG. 3).

[0036] With continued reference to FIG. 2, a method of designing aleadframe 30 according to the present invention includes configuring aplurality of leads 34 in a desired pattern, configuring a die mountingregion 32 adjacent a die connect end 33 of the leads, and configuring aplurality of offsets 36 that extend from major plane 38 of leadframe 30.

[0037] Leadframe 30 may be a modification of an existing leadframedesign, wherein offsets 36 are formed of excess material and areconfigured to extend transversely, adjacent an existing element of theleadframe, such as the leads 34, a tie bar, bus bar, or die paddle.Alternatively, with reference to FIG. 6a, an element or a portion of anelement of leadframe 30, such as lead 34, bus bar 46, or die paddle 49,may be bent in a desired direction and at a desired angle to defineoffset 36. In another variation, shown in FIG. 2a, leadframe 30 may beof a unique design wherein offsets 36 are designed as separate elementsof the leadframe.

[0038] Referring to FIG. 7, offsets 36 may be configured to extend fromleadframe 30 at a distance and in a direction which will maintain theposition of semiconductor device 50 within the cavity during theintroduction of a packaging material 76 into the cavity. Thus, thenumber and positioning of offsets 36 of leadframe 30 depend, in part,upon the desired manner of introducing packaging material 76 into cavity72. Configuring offsets 36 to extend proximate the periphery (i.e.,sides and ends) of leadframe 30 and, therefore, proximate the peripheralsurfaces of cavity 72 as mold 70, which has two halves 70 a and 70 b, isclosed around leadframe-semiconductor device assembly 55, may balancethe forces that the interior surface of the mold cavity and packagingmaterial 76 that is introduced into cavity 72 each exert against theleadframe.

[0039] With continued reference to FIG. 7, in configuring the length ofoffsets 36 and the direction in which offsets 36 will extend, variousother factors must also be considered, including, without limitation,the dimensions and tolerances of cavity 72 of mold 70 into whichleadframe 30 will be positioned for packaging or encapsulation.Preferably, the length and direction in which offsets 36 are configuredto extend will reduce the likelihood of causing damage to cavity 72 asmold 70 is closed over the leadframe-semiconductor device assembly 55.Offsets 36 may also be configured to deflect in response to the force ofthe inner surfaces of cavity 72 thereagainst, which may facilitate theproper orientation of semiconductor device 50 relative to the cavity andmay reduce or eliminate stress in the packaged semiconductor device thatis formed upon the introduction of packaging material 76 into thecavity.

[0040] Offsets 36 may also be configured to counteract predictablebending or warpage of a packaged semiconductor device, or otherwiseminimize internal stresses in the package. This may be done byconfiguring offsets 36 so that their position, length and direction ofextension counteract the tendency of a packaged semiconductor deviceincluding offsets 36 to warp or bend, or to eliminate other internalstresses within the packaged semiconductor device that may occur as thetemperature of the packaged semiconductor device changes and that arecaused by the different coefficients of thermal expansion of the variouscomponents of the packaged semiconductor device.

[0041] Referring to FIG. 8, offsets 36 may be configured to extend flushwith the outer surface of package 62 such that an edge of at least oneoffset 36 is exposed through an exterior surface of package 62. Offsets36 that extend from a semiconductor device 50 to a position proximatethe exterior surface of package 62 may facilitate the dissipation ofheat from die 50 and package 62. Additional heat may be dissipated frompackage 62 by contacting offsets 36 to an external heat spreader.

[0042] Referring again to FIG. 2, leadframe 30 may be fabricated frommaterials that are known in the art, such as copper (Cu), copper alloys,nickel (Ni), iron-nickel (Fe—Ni) alloys, Alloy 42, or other electricallyconductive materials. Similarly, leadframe 30 may be manufactured byprocesses that are known in the art, which typically include stamping oretching the leadframe material into the desired pattern. The leadframemay then be plated, deburred, or trimmed, as known in the art, in orderto impart same with desired characteristics. Offsets 36 may be bent in adesired direction and to a desired angle as known in the art, such asduring stamping of the leadframe or by another deformation operationsubsequent thereto. Similarly, other components of leadframe 30, such asleads 34, tie bars 45 (see FIGS. 2 and 2a), bus bars 47 or the diepaddle 49, may be bent as known in the art (see FIGS. 6a and 6 b). FIG.6b illustrates a die paddle 49 which includes offsets 36 extendingtherefrom in a cruciform configuration.

[0043] Referring again to FIG. 3, the bond pads 54 of semiconductordevice 50 may be operatively connected with corresponding leads 34 ofleadframe 30 by techniques that are known in the art, including, but notlimited to, wirebonds, TAB bonds, z-axis elastomer, solder, conductiveepoxy, and other electrically conductive connections. The operativeconnection of leadframe 30 to semiconductor device 50 forms aleadframe-semiconductor device assembly 55.

[0044] Turning again to FIG. 7, leadframe 30 may be packaged inaccordance with a packaging process of the present invention, whichincludes placing the leadframe within cavity 72 of mold 70 and injectingmolten packaging material 76 into the cavity under pressure. Asillustrated, mold 70 includes two halves 70 a and 70 b, each of whichdefine a cavity half 72 a and 72 b. Leadframe 30 is positioned overcavity half 72 a, 72 b of a mold half 70 a, 70 b, respectively. As moldhalves 70 a and 70 b are closed upon one another, leadframe 30 and anouter portion of leads 34 lie outside of cavity 72 and between moldhalves 70 a and 70 b while the remainder of leads 34, offsets 36, andother elements of leadframe 30 are enclosed within cavity 72. Offsets 36facilitate maintenance of the proper orientation of semiconductor device50 relative to cavity 72 as molten packaging material 76 is introducedinto cavity 72 through a gate 74 that is formed through mold 70, and iscontinuous with cavity 72. Molten packaging material 76 may beintroduced by techniques that are known and used in the art, including,without limitation, transfer molding techniques, injection moldingtechniques and casting. Similarly, offsets 36 may be positioned toeffect the flow of molten packaging material 76 into cavity 72 in amanner which reduces the force of the flowfront and the hydraulic forceof the packaging material against certain portions ofleadframe-semiconductor device assembly 55, such as the semiconductordevice 50 and any wire bonds 53 or other electrical connections betweeneach bond pad 54 and its corresponding lead 34.

[0045] As noted previously, if not trimmed adequately, when enclosedwithin a mold cavity, the perpendicularly extending offsets of someconventional leadframes will be forced directly against the innersurface of the cavity of a mold. The force of conventional,perpendicularly extending offsets against the inner surface of thecavity will cause the offsets to bend unpredictably and may cause theoffsets to buckle, which may alter the orientation of the semiconductordevice within the cavity and, therefore, within the package, and mayalso damage the surface of the cavity.

[0046] Referring again to FIG. 7, the non-perpendicularly extendingoffsets 36 of the leadframe 30 of the present invention reduce oreliminate the likelihood that an inner surface 73 of cavity 72 of mold70 will be damaged when the offsets 36, leads 34, semiconductor device50, and other components of the packaged semiconductor device are placedwithin the cavity and the mold closed therearound. If offsets 36 havenot been adequately trimmed, as mold 70 is closed on leadframe 30, theoffsets will flex toward or bend in a predictable direction, asillustrated by the arrows that are adjacent the offsets. Thus, thenon-perpendicular angle of extension of offsets 36 reduces the amount offorce that each offset 36 will apply to inner surface 73 of cavity 72 asmold halves 70 a and 70 b are forced together, thereby reducing oreliminating damage to the inner surface 73 of cavity 72 that may becaused by offsets 36.

[0047] Offsets 36 that extend from major plane 38 of leadframe 30 at anangle of about 45 degrees or less to the major plane are furtherdesirable since existing leadframe fabrication equipment can accuratelybend the offsets to such an angle. Consequently, the fabrication costsof the leadframe of the present invention are not significantlyincreased relative to the costs of fabricating conventional leadframes.

[0048]FIG. 8 illustrates a packaged semiconductor device 60 of thepresent invention, which includes a semiconductor device 50, leads 34operatively connected to the semiconductor device, offsets 36 thatextend transversely and non-perpendicularly from a major plane 38 of theleads, and a package 62 that covers, or encapsulates, at least a portionof each of the leads and the semiconductor device. Package 62 is formedof a packaging material 76, or encapsulant. Offsets 36 extend throughpackage 62 to a position that is proximate the exterior of the package.Offsets 36 may extend to a position that is flush with the exteriorsurface of package 62, such that an edge of an end of one or more of theoffsets is exposed to the exterior of the package.

[0049] Referring again to FIG. 2, the non-perpendicular angle at whichoffsets 36 extend from major plane 38 enhances the mechanicalreliability of the packaged semiconductor device 60 (FIG. 8). Suchnon-perpendicular extension of offsets 36 provides enhanced mechanicalreliability over conventional leads that lack offsets by reducing theamount that a packaged semiconductor device may bow, warp, bend, skew,or otherwise distort as the packaged semiconductor device undergoes atemperature change or is subjected to high temperatures, such as theambient operating temperature of the semiconductor device 50 containedtherein.

[0050] The non-perpendicular extension of offsets 36 from leadframe 30also provides advantages over conventional leads that includeperpendicularly extending offsets. The inventive leadframe consumes lessspace during storage than leadframes which include perpendicularlyextending offsets. As illustrated in FIG. 9, when stacked one uponanother, adjacent conventional leadframes 90 that include substantiallyperpendicularly extending offsets 92 are spaced apart from one another.In contrast, as shown in FIG. 10, leadframes 30, which includenon-perpendicularly extending offsets 36, may be compactly stacked, suchthat the adjacent surfaces of leadframes 30 are in substantial contactwith each other.

[0051] As shown in FIG. 11, an offset 36 having an angle of extension ofgreater than about 45 degrees from the major plane 38 of the leadframe30 may exert force on a corresponding offset 36′ of an adjacentleadframe 30′, causing one or both of the leadframes to bow.Accordingly, an offset 36 angle of extension of about 45 degrees or lessfacilitates optimally compact stacking of leadframes 30 against oneanother, while reducing or eliminating any bowing of the leadframes thatmay occur during stacking thereof.

[0052] Although the foregoing description contains many specifics, theseshould not be construed as limiting the scope of the present invention,but merely as providing illustrations of some of the presently preferredembodiments. Similarly, other embodiments of the invention may bedevised which do not depart from the spirit or scope of the presentinvention. The scope of this invention is, therefore, indicated andlimited only by the appended claims and their legal equivalents, ratherthan by the foregoing description. All additions, deletions andmodifications to the invention as disclosed herein which fall within themeaning and scope of the claims are to be embraced thereby.

What is claimed is:
 1. A method for designing a leadframe, comprising: configuring a plurality of leads to be at least partially located within a major plane of the leadframe; and configuring at least one offset for locational contact with a surface of processing equipment during processing of at least the leadframe to extend non-perpendicularly from said major plane, said at least one offset not comprising a lead.
 2. The method of claim 1, wherein said configuring said at least one offset comprises configuring said at least one offset to extend from a first side of said major plane.
 3. The method of claim 2, wherein said configuring said at least one offset comprises configuring at least another offset to extend from a second side of said major plane.
 4. The method of claim 1, wherein said configuring said at least one offset comprises configuring said at least one offset from a configured die mounting region of the leadframe.
 5. The method of claim 1, wherein said configuring said at least one offset comprises configuring said at least one offset to extend at an angle of about 45 degrees or less from said major plane.
 6. The method of claim 1, wherein said configuring said at least one offset comprises configuring said at least one offset to extend from the leadframe adjacent at least one of said plurality of leads.
 7. The method of claim 1, wherein said configuring said at least one offset comprises configuring said at least one offset for resilient locational contact with a surface of said processing equipment.
 8. A method for fabricating a leadframe, comprising: providing a sheet comprising electrically conductive material; forming a frame from said sheet; forming a plurality of leads from said sheet, each of said plurality of leads extending from said frame; and forming at least one offset for locational contact with a surface of processing equipment during processing of at least the leadframe to extend non-perpendicularly from a major plane of said frame, said at least one offset not comprising a lead.
 9. The method of claim 8, further comprising forming a tie bar to interconnect selected ones of said plurality of leads to each other.
 10. The method of claim 8, further comprising forming a die mounting region proximate die connect ends of at least some of said plurality of leads.
 11. The method of claim 10, wherein said forming said at least one offset comprises forming said at least one offset from said die mounting region.
 12. The method of claim 8, wherein said forming said at least one offset comprises forming at least two offsets that extend away from said major plane in different directions.
 13. The method of claim 8, wherein said forming said at least one offset comprises forming at least two offsets that extend from opposite sides of said major plane.
 14. The method of claim 8, wherein said forming said at least one offset comprises forming said at least one offset for resilient locational contact with a surface of said processing equipment.
 15. A method for manufacturing a leadframe, comprising: forming a frame from a sheet comprising electrically conductive material; forming a plurality of leads from said sheet, each of said plurality of leads extending from said frame and being located at least partially within a major plane thereof; and forming at least one offset for locational contact of the leadframe with a surface of processing equipment during processing of at least the leadframe to extend nonperpendicularly from said major plane of said sheet, said at least one offset not comprising a lead.
 16. The method of claim 15, further comprising forming a tie bar to interconnect at least some of said plurality of leads.
 17. The method of claim 15, further comprising forming a die mounting region proximate die connect ends of at least some of said plurality of leads.
 18. The method of claim 17, wherein said forming said at least one offset comprises forming said at least one offset to extend from said die mounting region.
 19. The method of claim 15, wherein said forming said at least one offset comprises forming at least two offsets to extend from said major plane in different directions.
 20. The method of claim 15, wherein said forming said at least one offset comprises forming at least two offsets to extend from opposite sides of said major plane.
 21. The method of claim 15, wherein said forming said at least one offset comprises forming said at least one offset for resilient locational contact with a surface of said processing equipment. 